1. Field of Invention
This invention relates to an illumination sensor for turning on and off a separately provided switch element in response to the brightness of ambient light and an electronic automatic on/off switch for turning on and off power supply to a load in response to the brightness of ambient light.
2. Related Art
Conventionally, an automatic on/off switch for detecting the brightness of ambient light and lighting a load when the ambient light becomes stipulated brightness or less has been provided. With an automatic on/off switch of this kind, a CdS cell has been widely used as an illumination sensor for detecting the brightness of ambient light. The automatic on/off switch of this kind is called a thermal type; a bimetal heater as a switch element is connected in series to the CdS cell and a contact inserted between a load and a power supply is opened and closed by means of the bimetal. Such a thermal-type automatic on/off switch has the advantage that it can be provided at low cost. However, cadmium is used for the CdS cell and therefore the automatic on/off switch using the CdS cell as the illumination sensor has a problem of a large load on the environment when it is manufactured and is discarded.
Then, a device using a photodiode array in place of the CdS cell to detect the brightness of ambient light is proposed to reduce the load on the environment when it is manufactured and is discarded. For example, JP-A-5-152924 describes a configuration wherein a photodiode array 1 is used as an illumination sensor for detecting the brightness of ambient light and a switching element 2 comprising two depletion-type MOSFETs connected in series is used as a switch element for turning on and off the feeding path from a power supply E to a load L, as shown in FIG. 81.
In the configuration, the load of cadmium on the environment is eliminated because the CdS cell is not used to detect the brightness and no power is required for controlling the switching element 2 and the number of parts is lessened because the photodiode array 1 of photovoltaic element is used.
By the way, the switching element 2 comprising two depletion-type MOSFETs is inserted between the power supply E and the load L in the configuration shown in FIG. 81 and thus the switching element 2 needs to have a large rated current capacity to use a load consuming large power. To drive the switching element 2 of a large rated current capacity, the electromotive force of the diode array 1 must also be enlarged. Since the electromotive force of one photodiode is constant, the number of photodiodes needs to be increased to provide a large electromotive force and consequently, the occupation area of the photodiode array 1 becomes large. That is, in addition to use of a high-cost switching element of a large rated current capacity as the switching element 2, a high-cost photodiode array 1 of a large area is also used as the photodiode array 1.
JP-A-5-152924 describes the fact that if the load capacity is large, the MOSFETs making up the switching element 2 are connected in parallel, thereby enlarging the current capacity of the switching element 2; however, if the gates and sources of two or more MOSFETs are connected in parallel, the capacity components of the gates and sources are also connected in parallel and thus it is feared that the capacity components may form a feedback path, resulting in an oscillation state. Moreover, if two or more MOSFETs are connected in parallel, the costs are increased as with use of MOSFET of a large rated current capacity and the MOSFET occupation area becomes large, leading to upsizing.
It is therefore an object of the invention to provide an electronic automatic on/off switch that can lessen a load on the environment, of course, and provide a comparatively large current capacity at low costs and an illumination sensor forming a part of the electronic automatic on/off switch with a switch element.
Illumination Sensor
According to a first aspect of the present invention, there is provided an illumination sensor comprising a photovoltaic element made of a solar battery for generating a voltage responsive to brightness of ambient light and a switching element comprising MOSFET being turned on or off in response to the output voltage of the photovoltaic element for opening or closing a separately provided switch element. According to the configuration, a solar battery is used as the photovoltaic element, whereby a circuit for applying a bias voltage as with a photodiode need not be provided and moreover a power supply is not required for controlling the switching element. Moreover, MOSFET is used as the switching element, so that low power is consumed and the switching element can be turned on and off by output of a small-sized solar battery. Further, CdS cells are not used and thus the ill effect of cadmium on the environment is not produced.
According to a second aspect of the present invention, in the illumination sensor as the first aspect of the present invention, the switching element is made up of two MOSFETs with sources connected and gates connected in common. In the configuration, the switching element can be used for an AC power supply.
According to the third aspect of the present invention, in the illumination sensor as the first aspect of the present invention, the photovoltaic element is a solar battery comprising a plurality of cells each having a pin structure connected in series on a single plane, the cells being formed on a single substrate. According to the configuration, the output voltage of the photovoltaic element can be enlarged without increasing the number of parts at the assembling time.
According to a fourth aspect of the present invention, in the illumination sensor as the first aspect of the present invention, an amorphous silicon solar battery having a sensitivity wavelength range of 400 to 700 nm, a peak wavelength in the vicinity of 500 nm, and a spectral sensitivity characteristic closely similar to the luminosity characteristic of a human being is used as the solar battery. According to the configuration, the operation of the switching element in response to the brightness of ambient light can be matched with the luminosity characteristic of a human being and control with no sense of incongruity is enabled. Moreover, an amorphous silicon solar battery is used, so that easy formation is enabled at comparatively low temperature on a comparatively inexpensive substrate of glass, silicon, etc., and costs can be reduced.
According to a fifth aspect of the present invention, the illumination sensor as the first aspect of the present invention further includes a light quantity adjustment member being placed in at least a part of an incidence path of ambient light on a light reception face of the photovoltaic element and having transmittance controlled by an external signal generated in response to opening or closing the switch element. According to the configuration, the light quantity adjustment member having transmittance controlled by an external signal responsive to turning on or off the switching element controlled in response to the brightness of ambient light is placed in the incidence path of ambient light on the photovoltaic element, so that it is made possible to give hysteresis to the relationship between the brightness of the ambient light and turning on/off the switching element. That is, an external signal is given so as to decrease the transmittance of the light quantity adjustment member when the ambient light is decreased, whereby it is made possible to lower the sensitivity when the quantity of the ambient light is small, and it is made possible to set so as to prevent a malfunction if light of headlights of an automobile, etc., is incident in the night. Since a delay element need not be placed between the solar battery and the switching element, when light quantity change of the ambient light is sufficiently large, the transmittance of the light quantity adjustment member can be immediately raised with no delay.
According a sixth aspect of the present invention, in the invention as the fifth aspect of the present invention, the light quantity adjustment member has a transmittance-type liquid crystal plate having transmittance changed in response to the strength of an electric field applied to liquid crystal. According to the configuration, a liquid crystal plate is used as the light quantity adjustment member; it is driven by an electric field and has very large impedance and thus consumes small power. That is, the switching element is driven by the output voltage of the photovoltaic element and the power required for the external signal for controlling the light quantity adjustment member is small, so that the illumination sensor can be operated with extremely small power. A polarizing plate is placed on each of the surface and the back of the liquid crystal plate and the transmittance of the polarizing plates and the liquid crystal plate is set based on the relative angle of a vibration face of light passing through the polarizing plates. According to the configuration, the transmittance is adjusted based on the positional relationship of the vibration face of light passing through the polarizing plates, so that it is made possible to make whole adjustment of the quantity of light incident on the photovoltaic element.
In a seventh aspect of the present invention, in the illumination sensor as the fifth aspect of the present invention, a monocrystalline silicon solar battery having a sensitivity wavelength range across a visible light area and a near-infrared light area and a peak wavelength in an infrared light area is used as the photovoltaic element and the liquid crystal plate used has a transmittance characteristic different between the visible light area and the infrared light area. The light quantity adjustment member has a transmittance-type liquid crystal plate having transmittance changed in response to the strength of an electric field applied to liquid crystal. According to the configuration, a liquid crystal plate is used as the light quantity adjustment member; it is driven by an electric field and has very large impedance and thus consumes small power. That is, the switching element is driven by the output voltage of the photovoltaic element and the power required for the external signal for controlling the light quantity adjustment member is small, so that the illumination sensor can be operated with extremely small power. According to the configuration, it is made possible to enlarge hysteresis for illumination light and lessen hysteresis for natural light by combining the spectral sensitivity characteristic of the photovoltaic element and the transmittance characteristic of the liquid crystal plate. That is, it is made possible to give a hysteresis characteristic such that no response is made if illumination light or light of headlights is incident as ambient light in the night and that a response is made immediately if the sunlight is incident at the crack of dawn.
In an eighth aspect of the present invention, in the illumination sensor as the fourth aspect of the present invention, a filter having transmittance different in a visible light area and an infrared light area is added to the incidence path of ambient light on the light reception face of the photovoltaic element. According to the configuration, the quantity of light incident on the photovoltaic element can be adjusted in response to the wavelength of light and it is made possible to provide any desired hysteresis characteristic.
In a ninth aspect of the present invention, the illumination sensor as the first aspect of the present invention further includes a control circuit being inserted between the photovoltaic element and the switching element for adjusting a response of the switching element to change in the output voltage of the photovoltaic element. According to the configuration, the response of the switching element to the output of the photovoltaic element can be adjusted.
In a tenth aspect of the present invention, the illumination sensor as the first aspect of the present invention further includes a package made of a molded article of a synthetic resin, the package being formed with connection terminals for connecting to an external circuit in one piece. According to the configuration, the connection terminals are projected on the package for easy mounting. Since the electric parts forming the illumination sensor are housed in the package of a molded article made of a synthetic resin, the illumination sensor can be miniaturized and moreover when the illumination sensor is built in any other unit, discrete electric parts need not be built in and the illumination sensor can be handled as one part. Moreover, the wiring length of the photovoltaic element and the switching element can be shortened by miniaturizing the illumination sensor, and external radiation noise can be prevented from causing the switching element to malfunction.
In an eleventh aspect of the present invention, in the illumination sensor as the tenth aspect of the present invention, the package is molded with a metal frame in one piece at the same time, the frame being formed with parts mounting parts where the connection terminals and electric parts are mounted and wiring parts forming electric paths between the connection terminals and the parts mounting parts. According to the configuration, the electric parts are mounted on the frame and the package is molded with the frame in one piece at the same time, so that manufacturing is easy and it is made possible to miniaturize as compared with the case for use with a print-circuit board, etc.
In a twelfth aspect of the present invention, the illumination sensor as the eleventh aspect of the present invention further includes a first seal member having a translucent property for sealing the photovoltaic element and a second seal member having a lightproof property for sealing the switching element. According to the configuration, both the photovoltaic element and the switching element are sealed with the seal members, whereby degradation caused by humidity, etc., can be suppressed and moreover the switching element is sealed with the seal member having a lightproof property, so that a malfunction or degradation caused by drawing light into the switching element can be prevented.
In a thirteenth aspect of the present invention, in the illumination sensor as the eleventh aspect of the present invention, the package is provided with a separation wall for separating the mounting part of the switching element and the mounting part of the photovoltaic element and a first seal member having a lightproof property for sealing the switching element and a second seal member having a translucent property for sealing the photovoltaic element are separated through the separation wall. According to the configuration, the switching element is sealed with the seal member not allowing light to pass through, so that the switching element can be prevented from being degraded because of the surrounding environment, and the photovoltaic element is sealed with the seal member having a translucent property, so that the photovoltaic element can be prevented from being degraded because of the surrounding environment. Further, the mounting part of the switching element and the mounting part of the photovoltaic element are separated by the separation wall, thus the seal member having a lightproof property for sealing the switching element and the seal member having a translucent property for sealing the photovoltaic element are not mixed; the accident in which the seal member having a lightproof property is drawn into the photovoltaic element for decreasing the quantity of light incident on the light reception face of the photovoltaic element can be prevented, and the state in which the elements are not completely sealed because each seal member is drawn into any other portion, whereby the amount of the seal member is lowered can be prevented from occurring.
In a fourteenth aspect of the present invention, in the illumination sensor as the eleventh aspect of the present invention, a light quantity adjustment member having transmittance controlled by an external signal generated in response to opening or closing the switch element is attached to the package so as to overlap at least a part of a light reception face of the photovoltaic element and is mounted on the parts mounting part and is electrically connected to the connection terminal. According to the configuration, an external control signal is input to the light quantity adjustment member, whereby the quantity of light passing through the light quantity adjustment member and incident on the light reception face of the photovoltaic element can be adjusted; for example, when the switching element is off, the quantity of light passing through the light quantity adjustment member is lowered, whereby hysteresis can be given to the response of the switching element to the brightness of ambient light when the switching element is turned on and off.
In a fifteenth aspect of the present invention, in the illumination sensor as the fourteenth aspect of the present invention, the light quantity adjustment member has a transmittance-type liquid crystal plate having transmittance changed in response to the strength of an electric field applied to liquid crystal and comprises a translucent seal member for sealing at least the periphery on the incidence side of ambient light on the liquid crystal plate. According to the configuration, the liquid crystal plate is vulnerable to the surrounding environment (particularly, humidity), but at least the periphery of the liquid crystal plate is sealed with the seal member, so that the liquid crystal plate can be prevented from being degraded due to humidity.
In a sixteenth aspect of the present invention, in the illumination sensor as the fourteenth aspect of the present invention, the light quantity adjustment member has a filter having a spectral transmittance characteristic different from that of the photovoltaic element, the filter being attached to the package so as to be opposed to the light reception face of the photovoltaic element. According to the configuration, the spectral characteristic of light incident on the photovoltaic element is corrected through the filter, so that the photovoltaic element can be provided with sensitivity to light in any desired wavelength area.
In a seventeenth aspect of the present invention, the illumination sensor as the first aspect of the present invention further includes a print-circuit board being formed with a wiring pattern for surface-mounting electric parts and provided with connection terminals for connecting to an external circuit and a package made of a translucent synthetic resin, integral with the print-circuit board so as to cover the side of the print-circuit board on which the photovoltaic element is mounted. According to the configuration, the electric parts forming the illumination sensor are mounted on the print-circuit board and thus can be easily mounted and the circuit pattern can be changed comparatively easily; illumination sensors of various specifications can be provided at low costs.
In an eighteenth aspect of the present invention, in the illumination sensor as the tenth aspect of the present invention, the package is a MID formed with parts mounting parts for mounting electric parts and wiring parts forming electric paths between the parts mounting parts and the connection terminals by metal plating. According to the configuration, it is made possible to place the electric parts stereoscopically and the illumination sensor can be miniaturized.
Electronic Automatic On/Off Switch
According to a nineteenth aspect of the present invention, there is provided an electronic automatic on/off switch comprising a photovoltaic element made of a solar battery for generating a voltage responsive to brightness of ambient light, a switching element comprising MOSFET being turned on or off upon reception of the output voltage of the photovoltaic element, and a switch element being inserted between an AC power supply and a load and controlled by the switching element so as to energize the load when brightness detected by the photovoltaic element is equal to or less than a stipulated value. According to the configuration, the brightness of ambient light is detected by the solar battery, so that the load on the environment at the manufacturing time or at the discard time is lessened as compared with use of CdS cells and moreover the solar battery produces a comparatively large output per area, thus MOSFET of voltage drive type consuming low power can be reliably driven without using an additional power supply or drive circuit. Moreover, when the brightness of ambient light is equal to or less than a stipulated value, namely, the surroundings become dark, the load is energized through the switch element separately provided from the switching element, so that it is not necessary to allow a load current to flow into the MOSFET, and if the load current is large, an inexpensive element having a smaller rated current capacity than the load current can be used as the switching element. Since the switch element is controlled by the switching element, an electromagnetic relay or a three-terminal bidirectional thyristor which has a comparatively large basic-angle current capacity and is comparatively inexpensive can be used as the switch element, and costs can be reduced as compared with the case where large-capacity MOSFET is used.
In a twentieth aspect of the present invention, in the electronic automatic on/off switch as the nineteenth aspect of the present invention, the switch element is an electromagnetic relay having a contact inserted between power supply and the load and a relay coil inserted between the power supply and the switching element. According to the configuration, the load is controlled by the electromagnetic relay, thus heat is little generated, a radiator plate required as a three-terminal bidirectional thyristor is used is not required, and a noise prevention circuit part is not required either. That is, the electronic automatic on/off switch can be more miniaturized and reduced in costs as compared with the case where a three-terminal bidirectional thyristor is used as the switch element.
In a twenty-first aspect of the present invention, in the electronic automatic on/off switch as the nineteenth aspect of the present invention, the switching element is made up of two MOSFETs with sources connected and gates connected in common. Thus, to adopt a configuration of supplying an alternating current to the switching element, a current can be prevented from flowing into the switching element through a parasitic diode of MOSFET when MOSFET is off, and the switching element can be turned off reliably.
In a twenty-second aspect of the present invention, in the electronic automatic on/off switch as the nineteenth aspect of the present invention, the photovoltaic element is a solar battery comprising a plurality of cells each having a pin structure connected in series on a single plane, the cells being formed on a single substrate. According to the configuration, the switching element is controlled based on the output voltage of the series circuit of the cells, whereby sensitivity can be enhanced and the solar battery can be handled as one part comprising a plurality of cells, so that the number of parts at the assembling time is not increased.
In a twenty-third aspect of the present invention, in the electronic automatic on/off switch as the nineteenth aspect of the present invention, an amorphous silicon solar battery having a sensitivity wavelength range of 400 to 700 nm, a peak wavelength in the vicinity of 500 nm, and a spectral sensitivity characteristic closely similar to the luminosity characteristic of a human being is used as the solar battery. According to the configuration, the amorphous silicon solar battery is used, so that easy formation is enabled at comparatively low temperature on a comparatively inexpensive substrate of glass, silicon, etc., and costs can be reduced. Since the spectral sensitivity characteristic is made closely similar to the luminosity characteristic of a human being, it is made possible to control the load almost matching the luminosity of a human being, and a sense of incongruity is not produced in control of the load.
According to the invention a twenty-fourth aspect of the present invention, there is provided an electronic automatic on/off switch comprising a photovoltaic element for generating a voltage responsive to brightness of ambient light, a voltage supervisory circuit being driven by the output voltage of the photovoltaic element and generating a binary signal in response to larger-than or smaller-than relation between reference voltage and the output voltage of the photovoltaic element, a switching element being turned on or off in response to the binary signal of the voltage supervisory circuit, and a switch element being inserted between a power supply and a load for turning on or off power supply to the load in response to turning on or off the switching element. According to the configuration, the response time of the switching element to change in the output voltage of the photovoltaic element is not adjusted, thus a malfunction is not caused by the change speed of brightness and moreover responsivity to change in the brightness can be enhanced.
In a twenty-fifth aspect of the present invention, in the electronic automatic on/off switch as the twenty-fourth aspect of the present invention, the voltage supervisory circuit comprises a reference voltage generation circuit for generating the reference voltage and a comparator for comparing the output voltage of the photovoltaic element with the reference voltage with respect to the larger-than or smaller-than relation. According to the configuration, the threshold value of brightness for operating the switching element can be set with accuracy.
In a twenty-sixth aspect of the present invention, in the electronic automatic on/off switch as the twenty-fifth aspect of the present invention, a series circuit of a plurality of diodes connected to the photovoltaic element via a resistor is used as the reference voltage generation circuit. According to the configuration, the reference voltage can be generated in a simple circuit configuration.
In a twenty-seventh aspect of the present invention, in the electronic automatic on/off switch as the twenty-fifth aspect of the present invention, the comparator comprises a feedback resistor for giving hysteresis to a threshold value for the output voltage of the photovoltaic element. According to the configuration, hysteresis is provided for the threshold value of brightness when the load is turned on/off, so that the load can be prevented from malfunctioning due to variation in the surrounding brightness.
In a twenty-eighth aspect of the present invention, in the electronic automatic on/off switch as the twenty-fifth aspect of the present invention, a threshold value switching element being turned on or off based on output of the comparator for giving hysteresis to a threshold value for the output voltage of the photovoltaic element is connected in parallel to at least some of the plurality of diodes. The threshold value switching element can be turned on or off, thereby changing the reference voltage for giving hysteresis to the threshold value of brightness when the load is turned on/off.
In a twenty-ninth aspect of the present invention, in the electronic automatic on/off switch as the twenty-fifth asepct of the present invention, the photovoltaic element is made of a solar battery comprising a plurality of cells connected in series and wherein a threshold value switching element being turned on or off based on output of the comparator for giving hysteresis to a threshold value for the output voltage of the photovoltaic element is connected in parallel to at least some of the plurality of cells. According to the configuration, the threshold value switching element can be turned on or off, thereby changing the electromotive force of the solar battery for providing hysteresis for the threshold value of brightness when the load is turned on/off.
In a thirtieth aspect of the present invention, the electronic automatic on/off switch as the nineteenth aspect of the present invention further includes a light emitting element for allowing light different from ambient light to be incident on the photovoltaic element and increasing the light quantity when the switch element is off as compared with that when the switch element is on. According to the configuration, when the surroundings are bright, the light emitting element is turned on, thereby allowing the ambient light and the light from the light emitting element to be incident on the photovoltaic element at the same time; when the surroundings are dark and bidirectional thyristor is turned on for energizing the load, the light emitting element is turned off. Thus, hysteresis can be given to the surrounding brightness and turning on/off the bidirectional thyristor and the on/off state of the bidirectional thyristor is not changed due to minute variation in the brightness of ambient light, namely, the operation of turning on/off the thyristor is stabilized.
In a thirty-first aspect of the present invention, in the electronic automatic on/off switch as the thirtieth aspect of the present invention, a series circuit of the light emitting element and a variable resistor is connected in parallel to the switch element. According to the configuration, when the surroundings are bright, the light emitting element is turned on, thereby allowing the ambient light and the light from the light emitting element to be incident on the photovoltaic element at the same time; when the surroundings are dark and bidirectional thyristor is turned on for energizing the load, the light emitting element is turned off. Thus, hysteresis can be given to the surrounding brightness and turning on/off the bidirectional thyristor and the on/off state of the bidirectional thyristor is not changed due to minute variation in the brightness of ambient light, namely, the operation of turning on/off the thyristor is stabilized. Moreover, the variable resistor is connected in series to the light emitting element, thus if the variable resistor is adjusted, the light emitting quantity of the light emitting element is adjusted and the hysteresis characteristic can be adjusted easily.
In a thirtysecond aspect of the present invention, in the electronic automatic on/off switch as the thirtieth aspect of the present invention, a series circuit of the light emitting element, a variable resistor, and the switching element is connected in parallel to the switch element. According to the configuration, when the surroundings are bright, the light emitting element is turned on, thereby allowing the ambient light and the light from the light emitting element to be incident on the photovoltaic element at the same time; when the surroundings are dark and bidirectional thyristor is turned on for energizing the load, the light emitting element is turned off. Thus, hysteresis can be given to the surrounding brightness and turning on/off the bidirectional thyristor and the on/off state of the bidirectional thyristor is not changed due to minute variation in the brightness of ambient light, namely, the operation of turning on/off the thyristor is stabilized. Moreover, the variable resistor is connected in series to the light emitting element, thus if the variable resistor is adjusted, the light emitting quantity of the light emitting element is adjusted and the hysteresis characteristic can be adjusted easily.
A thirty-third aspect of the present invention, the electronic automatic on/off switch as the thirtieth aspect of th present invention further includes a metal frame mounting the photovoltaic element and the switching element and a package made of a synthetic resin, molded with the frame in one piece at the same time, wherein the light emitting element is attached to the package and connection terminals formed continuously on the metal frame in one piece are projected from the package. According to the configuration, the connection terminals are projected on the package, so that mounting is easy.
In a thirty-fourth aspect of the present invention, the electronic automatic on/off switch as the nineteenth aspect of the present invention further includes a light quantity adjustment member being placed in at least a part of an incidence path of ambient light on a light reception face of the photovoltaic element and having transmittance lowered when the switch element is on as compared with that when the switch element is off. According to the configuration, once the on or off state of the switch element is changed, the on or off state can be made hard to be changed if the brightness of ambient light varies, and hysteresis can be given to turning on or off the switch element in response to the brightness of ambient light.
In a thirty-fifth aspect of the present invention, in the electronic automatic on/off switch as the thirty-fourth aspect of the present invention, the light quantity adjustment member has a transmittance-type liquid crystal plate having transmittance changed in response to the strength of an electric field applied to liquid crystal. According to the configuration, the applied voltage to the liquid crystal plate is adjusted, whereby the hysteresis characteristic can be adjusted.
In a thirty-sixth aspect of the present invention the electronic automatic on/off switch as the thirty-fifth aspect of the present invention further includes a base having one side to which the photovoltaic element and the switching element are attached and a cover for covering the one side of the base, the cover being provided in a part with a translucent plate for allowing ambient light to be incident on the photovoltaic element, wherein the liquid crystal plate is disposed between the photovoltaic element and the translucent plate. According to the configuration, the photovoltaic element and the liquid crystal plate are housed in the space closed by the base and the cover, so that the effect of stray light is hard to receive and it is made possible to set the hysteresis characteristic for ambient light with accuracy.
In a thirty-seventh aspect of the present invention, the electronic automatic on/off switch as the thirty-fifth aspect of the present invention further includes a base having one side to which the photovoltaic element and the switching element are attached and a cover for covering the one side of the base, the cover being provided with the liquid crystal plate in a part for allowing ambient light to be incident on the photovoltaic element. According to the configuration, the space between the photovoltaic element and the liquid crystal plate becomes the space closed by the base and the cover, so that the effect of stray light is hard to receive and it is made possible to set the hysteresis characteristic for ambient light with accuracy.
In a thirty-eighth aspect of the present invention, the electronic automatic on/off switch as the thirty-fifth aspect of the present invention further includes a metal frame mounting the photovoltaic element and the switching element and a package made of a synthetic resin, molded with the frame in one piece at the same time, wherein the liquid crystal plate is attached to the package so as to overlap a light reception face of the photovoltaic element and connection terminals formed continuously on the metal frame in one piece are projected from the package. According to the configuration, the metal frame and the synthetic resin package are molded in one piece at the same time, the frame is provided with the connection terminals, and the parts are mounted on the frame, so that any other circuit board is not required and the electronic automatic on/off switch can be miniaturized.
In a thirty-ninth aspect of the present invention, the electronic automatic on/off switch as the thirty-fifth aspect of the present invention further includes a print-circuit board mounting the photovoltaic element and the switching element, a holding frame made of a synthetic resin for holding the liquid crystal plate, and a case for housing at least the print-circuit board, wherein the holding frame is fixedly secured to either of the print-circuit board and the case. According to the configuration, the print-circuit board is used, so that mounting work is easy and moreover the holding frame holding the liquid crystal plate is fixedly secured to either of the print-circuit board and the case, thus the liquid crystal plate can be positioned reliably.
In a fortieth-aspect of the present invention, in the electronic automatic on/off switch as the twentieth aspect of the present invention, the power supply is an AC power supply, the electromagnetic relay is of AC-drive type, wherein the switching element is made up of two MOSFETs with sources connected and gates connected in common, and the drain of one MOSFET is connected to one end of a series circuit of the power supply and the relay coil and the drain of the other MOSFET is connected to an opposite end of the series circuit. According to the configuration, two MOSFETs are connected in inverse series, so that a current does not flow through a parasitic diode when MOSFET is off, and an alternating current can be shut off. Consequently, a simple circuit configuration is compatible with an AC power supply.
In a forty-first aspect of the present invention, in the electronic automatic on/off switch as the twentieth aspect of the present invention, the power supply is an AC power supply and the electromagnetic relay is of DC-drive type, further including a rectifier being inserted between a series circuit of the drain and source of the MOSFET and the relay coil and the power supply and a smoothing capacitor being connected in parallel to the relay coil. According to the configuration, the number of parts is increased as compared with the case where two MOSFETs are used, but an inexpensive DC electromagnetic relay can be used, the number of MOSFETs may be one, and it is not necessary to consider variations in the MOSFET characteristic. Moreover, the smoothing capacitor is used, whereby the delay time between the instant at which the switching element is turned off and the instant at which the contact of the electromagnetic relay is turned off can be set; for example, if the strong light of headlights of an automobile, etc., is applied for a short time in the night, the contact of the electromagnetic relay does not respond to the light, so that a malfunction can be prevented.